Structure and composition of the consolidated mud tube of Maldane sarsi (Polychaeta: Maldanidae)

Maldanid polychaetes can be important components of marine benthic communities, playing significant roles in particle subduction or sediment irrigation. Many maldanids are known to inhabit tubes consisting of sediments consolidated by mucus; the structure and composition of these tubes, and their potential impact on benthic environments, are poorly known. We examined the three-dimensional organization of Maldane sarsi tubes, using CT scanning together with analyses of sediment grain size and concentrations of Fe, Mn, organic carbon and bacteria in tube material. M. sarsi tubes consist of stacks of individual consolidated mud disks, surrounding a dense, continuous, inner tube. The tubes of M. sarsi contained fewer fine particles than surrounding sediments, and greater concentrations of Fe, Mn, organic carbon and bacteria, especially in the inner zone. These distributions suggest that tube irrigation affects Fe and Mn oxidation and precipitation in a narrow zone surrounding M. sarsi, and that mucous secretion and potential feeding activities (the hoeing of surface sediments) lead to increases in organic carbon and bacteria in the inner, and deepest parts of the tube. The finding of relict tubes, buried at up to 15 cm depth, indicates a relatively high longevity for these structures and suggests a potential importance in biogeochemical cycling.     

Variation in microbial biomass and community structure in sediments of peter the great bay (sea of japan/east sea), as estimated from fatty acid biomarkers

Variation in the microbial biomass and community structure found in sediment of heavily polluted bays and the adjacent unpolluted areas were examined using phospholipid fatty acid analysis. Total microbial biomass and microbial community structure were responding to environmental determinants, sediment grain size, depth of sediment, and pollution due to petroleum hydrocarbons. The marker fatty acids of microeukaryotes and prokaryotes - aerobic, anaerobic, and sulfate-reducing bacteria -were detected in sediments of the areas studied. Analysis of the fatty acid profiles revealed wide variations in the community structure in sediments, depending on the extent of pollution, sediment depth, and sediment grain size. The abundance of specific bacterial fatty acids points to the dominance of prokaryotic organisms, whose composition differed among the stations. Fatty acid distributions in sediments suggest the high contribution of aerobic bacteria. Sediments of polluted sites were significantly enriched with anaerobic bacteria in comparison with clean areas. The contribution of this bacterial group increased with the depth of sediments. Anaerobic bacteria were predominantly present in muddy sediments, as evidenced from the fatty acid profiles. Relatively high concentrations of marker fatty acids of sulfate-reducing bacteria were associated with organic pollution in this site. Specific fatty acids of microeukaryotes were more abundant in surface sediments than in deeper sediment layers. Among the microeukaryotes, diatoms were an important component. Significant amounts of bacterial biomass, the predominance of bacterial biomarker fatty acids with abundance of anaerobic and sulfate-reducing bacteria are indicative of a prokaryotic consortium responsive to organic pollution.     

江苏大丰海岸碱蓬滩潮沟及滩面的沉积动力特征

根据2002年7月在江苏大丰碱蓬滩潮沟观测的水文、悬沙、底质等资料,分析了潮沟的输水、输沙特征及悬沙和底质在粒径组成上的关系,结果表明,潮沟在流速、悬沙浓度、输水、悬沙输运、底质活动性等方面具有明显的涨落潮不对称.滩面归槽水占潮沟落潮输水量的33%,由此造成的悬沙输运量占潮沟落潮悬沙输运量的20%,这是导致潮沟涨落潮输水输沙不对称的主要因素.在一个潮周期中潮沟的净输水、净悬沙输运方向与滩面相反,指向落潮方向.悬沙和底质组成以粉砂和黏土为主,潮沟和滩面的悬沙粒径组成差别很小.悬沙是滩面底质的主要物质来源,两者在粒径组成上存在着必然联系,沉积物粒径与该粒级在底质中的含量与在悬沙中的含量之比具有明显的幂函数关系.     

鸭绿江河口地区沉积物的粒度变化及影响因素

通过对比鸭绿江河口不同地区柱状样的粒度参数及敏感组分变化规律,分析了河口不同地区沉积动力环境和沉积特征的差异;结合代表性柱状样的210Pb测年,分析了柱状样在不同时期自然和人类活动影响下的沉积特征变化。结果表明,西水道主要受潮流作用而含有泥沙互层,粒度参数变化小;西岸潮滩受潮流和波浪作用含有贝壳碎屑,并在顶部出现粗化层。近几十年来,鸭绿江河口地区沉积特征的变化主要由于人类活动对水沙入海通量的影响:1941年以前柱状样的波动沉积特征反映了河流山溪性特征;1941—1970(1980)年随水沙入海通量减少而呈现砂含量降低、粉砂增加的特征;1970(1980)—1990年由于水沙入海通量变化较小,而呈现沉积物组成和敏感组分保持稳定的特征;但1990年后随水沙入海通量的进一步降低,邻近河口区域的沉积物出现明显的粗化。     

Mineral provinces and matter provenance of the surficial sediments in the western Philippine Sea: implication for modern sedimentation in West Pacific marginal basin

The characteristics and distribution patterns of detrital minerals (0.063~0.125 mm) in marine sediments provide a significant indicator for the identification of the origin of sediment.The detrital mineral composition of 219 surface sediment samples was analysed to identify the distribution of sediments within the western Philippine Sea. The area can be divided into three mineral provinces: (I) province east of the Philippine Trench, the detrital minerals in this province are mainly composed of calcareous or siliceous organisms, with the addition of volcanogenic minerals from an adjacent island arc; (II) middle mineral province, clastic minerals including feldspar, quartz and colorless volcanic glass, sourced from seamounts with intermediate-acid volcanic rock, or erupting intermediate-acid volcano; (III) province west of the Palau—Kyūshū Ridge, the matter provenance within this province is complex; the small quantity of feldspar and quartz may be sourced from seamounts or erupting volcano with intermediate-acid composition, with a component of volcanic scoria sourced from a volcano erupting on the Palau—Kyūshū Ridge. it is suggested that, (1) Biogenic debris of the study area is closely related to water depth, with the amount of biogenic debris controlled by carbonate lysocline. (2) Volcaniclastic matter derived from the adjacent island arc can be entrained by oceanic currents and transported towards the abyssal basin over a short distance. The weathering products of volcanic rocks of the submarine plateau (e.g.,Benham Plateau) and adjacent ridges provide an important source of detrital sedimentation, and the influence scope of them is constrained by the intensity of submarine weathering. (3) Terrigenous sediments from the continent of Asia and the adjacent Philippine island arc have little influence on the sedimentation of this study area, and the felsic mineral component is probably sourced from volcanic seamounts of intermediate-acid composition.     

Seasonal distribution of bacteria in salt marsh sediments in North Carolina

The number and size of bacteria at four depths (0–1, 5–6, 10–11 and 20–21 cm) in a North Carolina salt marsh were minotored by direct counts for 13 months. The number of bacteria reached a maximum of about 1·4 × 10¹⁰ cells cm^?3 at the sediment surface in October, corresponding to the period of Spartina alterniflora die-back. Cell numbers were lowest and most consistent throughout the year at the 20 cm depth of sediment. Cell volumes averaged 0·2 μm³ at the marsh surface and decreased with depth. Mean standing crop of bacteria to a depth of 20 cm of sediment was about 14 g bacterial carbon m^?2. In surface sediments bacteria contribute up to 15% and algae up to 10% of total living microbial biomass as estimated by adenosine triphosphate (ATP). Bacteria were the major biomass component at sediment depths of 5, 10 and 20 cm. At all depths the microbial community contributes < 4% total organic carbon and < 8% of total nitrogen.     

长江河口近底层悬沙和沉积物的交换过程研究

大河河口的动力沉积过程一直是陆海相互作用研究的核心内容,其中水体泥沙的垂向交换是河口动力-沉积机制分析中的关键环节。基于2011年12月对长江河口及其邻近海湾采集的大范围、高密度的近底层悬沙、海床表层1~2cm(表层沉积物)和垂向向下约2~10cm的沉积物(次表层沉积物)同步3组303个样品,利用经验正交函数方法,对河口地区的悬沙和沉积物交换过程进行研究。结果表明:近底层水体悬沙的空间分布模式主要以粉砂粒级为主,空间分布差异性不大;表层及次表层沉积物的空间分布模式相似,但较近底层水体悬沙的分布复杂,存在明显的区域性特征,其中南汇边滩水域中部辐散区的沉积物表现为粗粉砂-细砂模式,其他区域由粉砂组分模式组成。近底层水体悬沙、表层和次表层沉积物的第一模态主要反映了粒径较细的泥沙运动,第二模态主要反映了粒径较粗的泥沙运动。在近底层水体悬沙与表层沉积物的垂向交换中,主要交换粒级为粉砂组分粒级。在表层沉积物与次表层沉积物的垂向交换中,南汇边滩中部辐散区的主要交换粒级为粗粉砂-细砂组分粒级,其他区域主要为粉砂组分粒级。     

Impact of lugworms (Arenicola marina) on mobilization and transport of fine particles and organic matter in marine sediments

We investigated the impact of sediment reworking fauna and hydrodynamics on mobilization and transport of organic matter and fine particles in marine sediments. Experiments were conducted in an annular flume using lugworms (Arenicola marina) as model organisms. The impact of lugworms on sediment characteristics and particle transport was followed through time in sediments experimentally enriched with fine particles (< 63 μm) and organic matter. Parallel experiments were run at low and high water current velocity (11 and 25 cm s^− 1) to evaluate the importance of sediment erosion at the sediment–water interface. There was no impact of fauna on sediment composition and particle transport at current velocity below the sediment erosion threshold. At current velocity above the erosion threshold, sediment reworking by lugworms resulted in dramatic particle transport (12 kg dry matter m^− 2) to an adjacent particle trap within 56 days. The transported matter was enriched 6–8 times in fine particles and organic matter when compared to the initial sediment. This study suggests that sediment reworking fauna is an important controlling factor for the particle composition of marine sediments. A. marina mediated sediment reworking greatly increases the sediment volume exposed to hydrodynamic forcing at the sediment–water interface, and through sediment resuspension control the content of fine particles and organic matter in the entire reworked sediment layer (> 20 cm depth).     

人工岛建设对海口湾沉积特征与泥沙运移的影响

近年来,人工岛被广泛应用于沿海地区的填海造陆工程以快速获得优质土地,但大面积的人工岛建设会对近岸海底沉积物的分布模式及输运过程产生重要影响.为认识人工岛建设后沉积物变化与运移特征,本文以南海明珠人工岛对海口湾的影响为例,根据人工岛建设前后分别在海口湾近岸采集的底质表层沉积物分析了沉积物特征变化,结合沉积动力分析及粒径趋...     

Influence of reach geomorphology on hyporheic communities in a gravel‐bed stream

The surface sediment, subsurface sediment, and hyporheos were sampled by freeze‐coring at three sites of contrasting geomorphology in a New Zealand gravel‐bed stream. No differences in size class composition were detected among the subsurface sediments of the three sites but the forced pool‐riffle (a stretch of stream where the sequence of pool and riffles is controlled by in‐channel bedrock outcrops) had significantly finer surface sediments than the other sites. The hyporheos of all sites was dominated numerically by insects, including nymphs of Deleatidium and Oniscigaster, and chironomid larvae. Of the non‐insect taxa, Isopoda, Oligochaeta, and Acari were most common. No significant differences existed between total invertebrate density or taxon richness at the sites. Aoteapsyche was found only in the plane bed site, whereas Nesameletus was found only in the forced pool‐riffle. Psilochorema and Nematoda occurred at significantly lower densities in the forced pool‐riffle than in the plane bed or floodplain sites. For most taxa, local variation within a site was greater than that between sites. Total invertebrate density was highest near the sediment surface but no significant differences were found between the three sites in this or any other depth layer. Significant site‐depth interactions were obtained for three taxa (Zelandobius, Ostracoda, and Oligochaeta) indicating that local geomorphology may result in differential depth distributions of hyporheic species.     

Temporal variation in the vertical distribution of microphytobenthos in intertidal flats of the Nakdong River estuary,Korea

The vertical distribution of microphytobenthos (MPB) was investigated in intertidal flats of the Nakdong River estuary over different temporal periods. The MPB biomass were measured as chlorophyll a concentration in the sediment, and monitored at two different depth scales. From August 2006 to August 2007, monthly sampling was carried out at four sites to a depth of 10 cm. The vertical distribution exhibited an exponential decline with depth and the slope was closely related to sediment composition and MPB biomass in the surface sediment. The two slightly muddy sand (5–25% mud, <63 μm) sites presented similar trends of seasonal variation to a sediment depth of 10 cm, and no statistical difference was observed in their initial values and the slope of the exponential curves applied to each data set. The site with higher mud content also had higher surface biomass, and the fitted exponential curve had a larger slope than sites with more sand content. The seasonal variations of phaeo-pigments compared to chlorophyll a revealed higher grazing stress on the MPB in summer at the three slightly muddy sand sites, and low grazing stress all year around at the sand (<5% mud) site. In January, April and October 2007, and January 2008, diurnal sampling was conducted at hourly intervals at one slightly muddy sand site. The investigation in January 2007 which was conducted at 1 cm intervals to a depth of 10 cm sediment showed the migration mainly existed in the upper 1 cm. The other diurnal sampling was undertaken to a 1 cm depth at 0.5 mm intervals. An evident migratory rhythm was present, with migration up to the surface during daytime emersion and down into deeper sediment during night and high tide submersion. Migrating cells could reach sediments as deep as 6 or even 10 mm. When the visible thick biofilms formed, the migratory rhythm changed by keeping higher biomass at the surface even at night and during high tide submersion. Generally, the MPB surface biomass was an important factor in structuring the MPB vertical distribution. The vertical distribution to depths of 10 cm was closely related to the sediment composition over the long term, while the MPB migration influenced the vertical distribution over the short term in the top 1 cm of the sediment.     

青岛市灵山湾海水浴场表层沉积物粒度冬季变化特征及其原因

于2013年11月、2014年1月及3月在青岛市灵山湾海水浴场进行了3次表层沉积物采样,对粒度组分和粒度参数平面分布的变化进行了分析。结果表明,本区沉积物整体有变粗的趋势,细砂组分特别是极细砂和粉砂组分含量下降明显,分选性变好,正偏态及高峰度分布区扩大,粒度参数高值分布区被消除。粒径趋势分析表明,在涨潮流与强盛的冬季风驱动的风浪、沿岸流的综合作用下,研究区沉积物总体呈北东-南西向沿岸输运,运移趋势变化受到波浪、潮流水动力条件与地形相互作用的影响。短期的波能变化足以改变沙滩地貌,从而影响表层沉积物的分布。可为浴场维护提供理论依据。     

沉积物粒度组分空间预测的神经网络残余kriging方法

针对近海表层沉积物粒度组分空间变异的尺度差异性,提出了基于广义回归神经网络残余kriging的沉积物粒度组分空间预测方法,并以海州湾沉积物粒度数据为基础,分析了其在沉积物粒度组分空间预测和底质类型制图中的应用效果。结果表明,广义回归神经网络残余kriging方法能够获得比普通kriging方法更高的沉积物粒度组分空间预测精度,并且其底质类型的总体空间预测精度达到85%以上,相应的Kappa系数也在0.8以上,显示底质制图的预测类型与样本的实测类型具有较高的一致性。新方法对于开展定量化的沉积物粒度组分空间预测和底质类型制图具有参考价值。     

Composition and bacterial utilization of free amino acids in tropical mangrove sediments

The composition and bacterial utilization of dissolved free amino acids (DFAA) in tropical mangrove sediments was examined. Amino acid concentrations (300–900 ng total DFAA ml⁻¹) and composition were similar to that of other organic-rich, anaerobic sediments with lowest and highest concentrations in the low and mid intertidal zones, respectively. The non-protein amino acid, β-glutamic acid, rarely reported in previous studies, was found as a major component of the interstitial DFAA pool. Intracellular amino acids from some cultured strains of sulphate-reducing bacteria (e.g. Desulfobacter app) showed the presence of β-glutamic acid as a major cellular constituent suggesting that these bacteria may be a source of this amino acid in mangrove pore waters. In high intertidal sediments, bacterial growth rates (μ) correlated significantly with total DFAA concentrations with depth.Amino acid concentrations and composition differed significantly between sediments and overlying tidal waters. Flux chamber experiments showed negligible amino acid flux out of the sediments in untreated chambers, but rates of amino acid flux ranged from 27 to 69 mgN m⁻² day⁻¹ (= 81–207 mg C.m⁻² day⁻¹) in chambers where poisons were applied to the sediment surface. Such fluxes could account for between 9–38% and 5–19% of the nitrogen and carbon required to support the levels of bacterial productivity measured in surface (0–1 cm) sediments. These experiments suggest that bacterial populations in surface sediments are capable of utilizing all of the amino acid flux to the sediment-water interface in tropical mangroves.     

南海表层沉积物与水柱中沉降颗粒物对比研究及其古环境再造意义

分析了南海62个表层沉积物样品中生源(有机质、碳酸钙和蛋白石)和非生源(岩源物质)组分的含量变化和分布特征,并以沉积学分区为基础,结合5个沉积物捕获器站位,将南海划分为N、C-NE、SW和S 4个区域,对比分析了各区表层沉积物和水柱中沉降颗粒物中各组分含量、沉积通量分布特征和变化,探讨了表层沉积物的输出生产力、沉降颗粒物的初级生产力及真光层下100 m输出生产力三者之间的对应关系.结果显示:南海4个海域表层沉积物中各组分平均含量多数低于沉降颗粒物中的平均含量,而碳酸钙、岩源物质的沉积通量却多数高于沉降颗粒物中的沉积通量,分析得出表层沉积物中各组分平均含量和沉积通量不仅受水柱中各组分输出量影响,还受到陆源物质输入、溶解作用和上层水体营养盐影响.南海表层沉积物中生源组分沉积通量大小对应其输出生产力的大小.但是,由于陆源有机质、生源颗粒侧向漂移的影响,表层沉积物的输出生产力大小分布并不完全对应沉降颗粒物的初级生产力大小分布,尽管南海真光层下100 m输出生产力与沉降颗粒物的初级生产力比值与世界大洋"f"比平均值基本一致,但是,明显低于表层沉积物的输出生产力大小,只有在沉降颗粒物的初级生产力较高区域,真光层下100 m输出生产力大小才最接近表层沉积物的输出生产力大小.     

Characteristics of resuspended sediment from Georges Bank collected with a sediment trap

A sediment trap was deployed 3 m from the bottom at a water depth of 62 m on the southern flank of Georges Bank (41°02·2′N, 67°33·5′W) from 30 September 1978 to 10 March 1979 to qualitatively determine the size of sediments resuspended from the bottom by winter storms and to determine if seasonal changes in the phytoplankton could be observed in the trapped sediment.Bulk X-ray analyses of the trapped sediment showed layers of distinctly different textures preserved in the collection vessel. The median grain size of sampled layers ranged from 2·7 to 6·5 φ (fine sand to silt), but all layers contained a pronounced mode in the 3 φ (fine sand) range. Nine layers containing relatively large amounts of sand were present. The sand content was 75% in the coarest layers and about 32% in the fine layers. The median grain size of bottom sediments at the deployment site was considerably coarser than the trap samples, although the dominant grain size was also 3 φ.Average bottom-current speeds during the deployment period were about 30 cm s^?1 with a range of 10 to 50 cm s^?1. Bottom stress, computed from the observed currents and waves, suggest that 11 storms caused sufficient stress to resuspend 3 φ-sized sediments, in good agreement with the nine layers of relatively coarse sediments collected in the trap. Surface waves had to be included in the calculation of bottom stress because the bottom currents alone were insufficient to cause the resuspension of 3 φ-sized sediment.The trapped sediments contain numerous diatoms and coccoliths that are typical of late fall and winter assemblages. No clear seasonal difference in the flora was noted among sampled layers, probably due to the large influx of resuspended material and a reduced primary flux during this period. An undescribed species of Thalassiosira (G. Fryxell, personal communication), and siliceous scales of unknown systematic position were observed at all levels.     

Granulometric selectivity in Liza ramado and potential contamination resulting from heavy metal load in feeding areas

The stomach contents of thin-lipped grey mullets Liza ramado were analysed in terms of granulometric composition and compared to the sediment of potential feeding areas in the Tagus estuary. Total organic matter (TOM) content and heavy metal content were determined in the surface sediment of three areas and eight trace elements were quantified: Cd, Co, Cr, Cu, Hg, Ni, Pb and Zn. The three sampled areas did not differ in TOM; and the heavy metal content was below Effects Range-Low level for most elements. The mean observed concentrations were present in the following sequence: Zn > Pb > Cr > Cu ≈ Ni > Co > Cd > Hg. Stomach contents granulometric composition provided information about the feeding selectivity of the mullets. Sediment fractions with particle size between 20 and 50 μm are preferred, independently of the fishes' length. Smaller standard length (SL) fishes have a higher positive selection of fine grained sediments than those with a larger SL. Finer fractions usually have higher concentration of heavy metals, which makes younger specimens of the thin-lipped grey mullet potentially more exposed to heavy metal load in the estuary. Metal concentration was not independent from the sampling point, presenting higher values near the margins and the estuary tidal drainage system. This means that during the first period of each tidal cycle, the mullets will feed first on the most contaminated areas, as a consequence of their movement following the rising tide to feed on previously exposed areas.     

Grain size and depositional environment as predictors of permeability in coastal marine sands

More than half of the surface sediments covering the continental shelves are sandy, which may permit substantial sub-seafloor pore water advection. Knowledge of sediment permeability is required for quantifying advection and associated solute transport, but studies of marine sediments typically report grain size analyses rather than permeability. Here data from 23 studies were examined to determine the range in permeabilities reported for sublittoral marine sands and to assess the utility of permeability–grain size relationships in this setting. In the resulting database, the permeability of small (∼30 cm) undisturbed cores collected from the sea floor all fell between 2 × 10⁻¹² and 4 × 10⁻¹⁰ m², a range where advective transport induced by wave and current action should be pervasive. The range in grain size was very similar for near-shore (<10 m water depth) and continental shelf samples (>10 m water depth), but the permeability of the continental shelf samples was consistently lower for the same median grain size. Empirical permeability–grain size relationships generated a poor fit (r² = 0.35) for the aggregate data, but separate relationships for near-shore and continental shelf samples were significantly better, r² = 0.66 and 0.77, respectively. Permeability–grain size relationships thus may be useful for sublittoral sands, but a larger database needs to be accumulated before reliable fit parameters and variability can be predicted. Thus it is recommended that permeability be routinely determined when characterizing sedimentological properties of marine sand deposits. Concurrent determinations of sediment bulk density and porosity may further improve estimates of permeability.     

闽江下游河口区及其邻近海域表层沉积物的地球化学特征

闽江是我国东南沿海地区最大的河流,年径流量位居全国第3位。对采自闽江下游及闽江口邻近海域的沉积物分析表明,沉积物以SiO2含量高、Al2O3等组分的含量较低为特点。样品中碎屑矿物主要是石英、斜长石、正长石、白云母和绿泥石。从SiO2看,闽江沉积物与石英砂岩的成分较接近,不同于浅海沉积物,与黄河、长江、珠江三大河流也有较大差异。地形地貌及水动力条件控制沉积物粒度的分布,粒度又控制沉积物的组分分布。总体表现为,由陆向海,呈SiO2逐渐降低、Al2O3等组分升高的趋势。人类活动对闽侯段及闽江北港到马江段河流沉积物的影响也不容忽视。闽江流域的源区特征、水动力条件和搬运距离以及物理化学条件与生物作用对沉积物的改造,使得沉积物组分间具有良好的相关性。     

Biodiversity and community composition of sediment macrofauna associated with deep-sea Lophelia pertusa habitats in the Gulf of Mexico

Scleractinian corals create three-dimensional reefs that provide sheltered refuges, facilitate sediment accumulation, and enhance colonization of encrusting fauna. While heterogeneous coral habitats can harbor high levels of biodiversity, their effect on the community composition within nearby sediments remains unclear, particularly in the deep sea. Sediment macrofauna from deep-sea coral habitats (Lophelia pertusa) and non-coral, background sediments were examined at three sites in the northern Gulf of Mexico (VK826, VK906, MC751, 350–500 m depth) to determine whether macrofaunal abundance, diversity, and community composition near corals differed from background soft-sediments. Macrofaunal densities ranged from 26 to 125 individuals 32 cm⁻² and were significantly greater near coral versus background sediments only at VK826. Of the 86 benthic invertebrate taxa identified, 16 were exclusive to near-coral habitats, while 14 were found only in background sediments. Diversity (Fisher’s α) and evenness were significantly higher within near-coral sediments only at MC751 while taxon richness was similar among all habitats. Community composition was significantly different both between near-coral and background sediments and among the three primary sites. Polychaetes numerically dominated all samples, accounting for up to 70% of the total individuals near coral, whereas peracarid crustaceans were proportionally more abundant in background sediments (18%) than in those near coral (10%). The reef effect differed among sites, with community patterns potentially influenced by the size of reef habitat. Taxon turnover occurred with distance from the reef, suggesting that reef extent may represent an important factor in structuring sediment communities near L. pertusa. Polychaete communities in both habitats differed from other Gulf of Mexico (GOM) soft sediments based on data from previous studies, and we hypothesize that local environmental conditions found near L. pertusa may influence the macrofaunal community structure beyond the edges of the reef. This study represents the first assessment of L. pertusa-associated sediment communities in the GOM and provides baseline data that can help define the role of transition zones, from deep reefs to soft sediments, in shaping macrofaunal community structure and maintaining biodiversity; this information can help guide future conservation and management activities.